Engine Clearing Procedures in Toronto

[hawk37]

Toronto ATIS often mentions that aircraft requiring an engine clearing procedure before takeoff must advise atc on initial taxi

I tried google, and this site's search function but with little clarification

Is this a procedure to shed ice from fan blades?

Or is this a procedure to help prevent traces of de/anti icing fluid from entering the airconditioning system at a critical time on takeoff?

Thanks in advance for replies

[Intruder]

Is this a procedure to shed ice from fan blades?

In general, yes. Some engines require a runup as long as 30 seconds before takeoff when in potential icing conditions and engine anti-ice is in use.

[hawk37]

I thought there may be some replies on the de/anti icing fluid entering the airconditioning system idea. Guess not?

Thanks Intruder